“Humans are terrible athletes in terms of power and speed,” said Lieberman, “but we’re phenomenal at slow and steady. We’re the tortoises of the animal kingdom.”

When we think of running, it’s easy to conjure up images of cheetahs chasing down antlers in the jungle, or a horse sprinting through the racetrack, or a lion hunting down the prey. Not many would think of human beings.

But there’s a difference between being fast, which requires tremendous power, and being endurant, which requires long and repeated contraction of muscles under stress. While cheetahs and lions can break into a sprint of incredible speed, their muscles build up tremendous residue of lactic acids that require a long period of cool down. Lactic acid is the chemical that triggers soreness.

In contrast, human bodies are efficient for long distance running. While our top speed are nothing to boast of, our muscles can endure long periods of stress, allowing us to run at a moderate speed for hours at a time.

“That evidence belies the long and firmly held belief that humans are the animal world’s biggest wimps”, writes the Harvard Gazette, “and, if not for our big brains and advanced weapons, we’d be forced to subsist on fruits and vegetables, always in danger of being gobbled up by fiercer predators.”

But we’re not wimps. Besides our big brains, we have our physical endurance to boast of (though some members of our species can boast neither). Anthropologists have long theorized that early humans hunted animals down by stalking and tiring down the prey, rather than out-chasing and assaulting them. Our muscles seem to support that theory.

“While animals get rid of excess heat by panting, they can’t pant when they gallop”, Lieberman said. To successfully hunt down an animal, our ancestors didn’t have to run faster than the prey. All they had to do is keep tailing them and slowly closing the distance over an extended period of time. The prey will exhaust, creating the ideal situation for a close-ranged assault. Liberman describe the hunting style of early humans

The intense heat from prolonged running can literally fry most animals’ brains. Humans, on the otherhand, has a highly developing cooling system, using sweating as a regulatory control on the body’s temperature. When the sweat evaporates, heat is transferred from the body into the surrounding.

“We can run in conditions that no other animal can run in,” writes Liberman. That can be exemplified by the diverse lifestyles that have appeared on this planet, from hunting down deers in the blazing African sun, or stalking moose in the freezing Siberian landmass.